During investigation of a gastroenteritis outbreak in a chronic care institution, Norwalk virus was found in stool specimens from two individuals and bacterial isolates presumptively identified as Bacillus cereus were isolated from four individuals (including one with Norwalk virus) and spice. Phage typing confirmed all Bacillus clinical isolates were phage type 2. All clinical isolates were subsequently identified as B. thuringiensis when tested as a result of a related study (L. Leroux, personal communication). Eight of 10 spice isolates were phage type 4. All B. cereus and B. thuringiensis isolates showed cytotoxic effects characteristic of enterotoxin-producing B. cereus. An additional 20 isolates each of B. cereus and B. thuringiensis from other sources were tested for cytotoxicity. With the exception of one B. cereus, all showed characteristic cytotoxic patterns.

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A total of 174 strains of Escherichia coli serotype 0157:H7 representing human isolates obtained from outbreaks and sporadic cases of hemorrhagic colitis, hemolytic-uremic syndrome, and nonbloody diarrheal illnesses as well as from asymptomatic carriers across Canada and the United States were examined. E. coli serotype 0157:H7 possessed distinct biochemical markers, a 100% negative reaction for P-glucuronidase and sorbitol, and a 100% positive reaction for raffinose and dulcitol; all strains otherwise were biochemically typical of E. coli. The vast majority (97%) of the strains were susceptible to commonly used antimicrobial agents. Au strains produced readily detectable levels of Verotoxin; however, with polymyxin extraction, nearly 50% of the strains showed up to a 10-fold increase in the toxin level. None were found to mediate hemagglutination of human group A erythrocytes with or without D-mannose. The majority (-70%) of the strains showed localized and diffuse adherence to HEp-2 cells and Henle 407 cells, and the adherence patterns were not very different from those observed among other E. coli strains. Twenty phage types were recognized, with phage types 1 and 2 accounting for 65% of the test strains. Plasmid analysis indicated three basic plasmid profiles: profile I was characterized by 68.7-and 4.2-megadalton (MDa) plasmids (62% of strains), profile Il was characterized by 66.2-and 1.8-MDa plasmids (20% of strains), and profile III was characterized by a 62.5-MDa plasmid (18% of strains). A small number (19%) of the strains carried at least one additional plasmid over the basic complements, and these could be considered to constitute a miscellaneous category. None of the abovedescribed characteristics of E. coli serotype 0157:H7 could be directly correlated with one another, with the nature of infection, or with the geographical distribution of strains. Escherichia coli serotype 0157:H7, initially recognized in 1982 in the United States (34, 42), has now emerged as an important enteric pathogen of considerable public health significance in Canada, the United States, and the United Kingdom, with many outbreaks and numerous sporadic cases of hemorrhagic colitis, hemolytic-uremic syndrome, and diarrheal illness occurring in nursing homes, day-care centers, schools

85 Vibrio phages, 84 of them tailed and 1 filamentous, were surveyed. The tailed phages belonged to six basic morphotypes and to the Myoviridae, Siphoviridae, or Podoviridae families. 63 phages were classified into 18 species. The filamentous phage is a member of the Inovirus genus of the Inoviridae family. Vibrio phages are very heterogenous and include some morphologically interesting viruses. Several Vibrio phages closely resemble phages of other gram-negative bacteria, possibly indicating phylogenetic relationships between their hosts.